The effect of the small-molecule luteinising hormone receptor agonist, LHR-Chap, on receptor trafficking and G protein-independent signalling.

Abstract

Sexual development and reproductive function are controlled by the hypothalamic-pituitary-gonadal axis which regulates secretion of luteinising hormone (LH) and follicle stimulating hormone (FSH) which travel through the circulation to the gonads where they bind to their respective receptors, the luteinising hormone receptor (LHR) and follicle stimulating hormone (FSHR). The LHR forms part of the G protein-coupled receptor (GPCR) superfamily. Upon ligand binding, GPCRs undergo a conformational change enabling them to couple to specific families of intracellular heterotrimeric G proteins. Activation of G protein-dependent signalling pathways has been shown to stimulate the mitogen activation protein kinase signalling (MAPK) cascade. Interestingly, signalling through GPCRs also occurs in a G protein-independent manner. Typically, this is mediated by β-arrestin binding to the receptor which are also involved in the regulatory processes of GPCR desensitisation, internalisation and downregulation. Gonadotropins have been used extensively in assisted reproductive therapies. The focus of several drug discovery efforts has been to develop non-peptide analogues for these hormones in order to improve convenience of treatment and production. One such compound, LHR-Chap, shows great therapeutic potential. However, not much is known about the signalling mechanisms activated in response to this compound. Therefore, the aim of the present study was to examine the effects of LHR-Chap on LHR induced signalling pathways and trafficking. The data demonstrated biased agonism of LHR-Chap, as it was shown that, while the native cognate hormone activated the cAMP signalling pathway, the IP3 signalling pathway and the ERK/MAPK signalling pathway, LHR-Chap only stimulated the cAMP signalling pathway. Furthermore, evidence of differential LHR trafficking in response to treatment with native hormone vs LHR-Chap was also observed. These findings highlight the importance of further studies relating to LHR signalling/trafficking in response to LHR-Chap.